THE IMPACTS ON COASTAL LAGOONS
The lagoons of El Carmen-Pajonal-Machona in Cardenas and the lagoon of Mecoacan in Paraiso, all in the state of Tabasco, are elements of one of the most important coastal lagoon system with the highest production of oysters. Mexico occupies sixth place in the the world for oyster production and the state of Tabasco produces 36% of the national production. These rich lagoon systems have been severely impacted by the activities of the Mexican government owned oil company, Petroleos Mexicanos (PEMEX), for over 25 years, and no action has been take until now to restore the ecosystems and to carry out the agreements between the affected communities and the company.
In addition to the impacts generated by the discharge of oil related products, the installations of the petroleum industry have had very serious impacts on the coastal lagoons and wetlands of almost the whole territory of the state of Tabasco. The dredging, opening of sandbars, road construction, extraction of materials and filling activities, which are part of the oil exploration and production, have brought serious alterations to the complex hydrological systems of the region.
Salinization of the El Carmen-Pajonal-Machona lagoons
The greatest environmental and subsequently social and economical disaster has been generated by the salinization of the El Carmen-Pajonal-Machona lagoon system and of thousands of acres both near-by and far away which used to be productive and now suffer from serious deterioration.
The opening of a mouth through the Panteones sandbar which closes the Machona lagoon, by the Agriculture and Hydraulic Resources Ministry (Secretaria de Agricultura y Recursos Hidraulicos, SARH) in 1975, increased the salinity of the lagoon system; it was supposedly expected to increase the production of oysters. Nevertheless, the coastal dynamics and specially the huge number of PEMEX installations developed before and after the opening of the sandbar stir up uncontrolled salinization of the lagoon system and of thousands of acres of productive land.
Between 1965 and 1972, PEMEX built the Arroyo Verde drain, 16 feet deep, 37 meters wide and with 60 intercommunicating channels through the El Carmen-Pajonal-Machona and Redonda lagoon system to facilitate the access of the drilling barges and boats transporting chemicals. These dredging works, and the opening of the Tupilco artificial sandbar by PEMEX, made a significant contribution to the salinization of the lagoon system, and of the agricultural and grazing land. As a matter of fact, there are enough evidence available to prove that PEMEX contracted several time services to dredge the Panteones mouth, even after the disastrous impact of salinization on the ecosystem and the communities was already known.
Several government agencies have called during several years for the closure or stabilization of the Panteones mouth. In 1982, the Fisheries Ministry presented a project for the closure of the sandbar including a cost estimate. A year later, Blair Kinsman, an oceanographer, proposed five methods for the closure of the sandbar. In 1987, the SARH proposed the closure of the sandbar as a possible solution to the problems in the lagoon system. In 1991, the Ecology Department of the state of Tabasco office of the Environment Ministry proposed to stabilize the incoming water through the Panteones mouth in the sandbar.
Neverthless, in spite of the damages done and the proposals presented, nothing was done whatsoever. The extension of the resulting salinization has gradually increased, affecting between 200,000 and 250,000 acres. PEMEX has refused to assume its responsibility in the environmental disaster, regardless the recommendation 100/92 of the National Commission for Human Rights (Comision Nacional de Derechos Humanos, CNDH) which establishes clearly the guilt of the state owned industry.
The oyster crisis in Mecoacan
Oyster production decreased in the first years of this decade, just after one of PEMEX burners, located in the Mecoacan lagoon, shut down, spilling a large amount of fossil fuel into the lagoon. PEMEX did not assume the responsibility for the mortality in the oyster beds and has not fulfil the agreements to relocate the burners.
Around 1978 onward, the port of Dos Bocas, the PEMEX maritime terminal, began operations, and a sewage drain to the Mecoacan lagoon was installed in a place known as "El Chenaque". Some burners were also built along the bank of the lagoon.. In November 1991 one of these burners shut down, spilling a considerable amount of oil into the lagoon and damaging inmediately the area where the oysters are fastened, near the burner and the village of Tomo Largo, where some domestic animals died; and plants, buildings, automoviles and boats were damaged. a farther effect on the remaining oyster population stir up a high mortality rate in the lagoon.
PEMEX again did not accept the blame and contracted the services of some research institutions. Other independent studies were carried out and provided information on the lagoon but the problem was not solved.
The existing information put forth enough data to identify two main causes for the oyster mortality: one natural and one artificial. During the seventies, high mortality in the east part of the lagoon was related to a decrease of salinity brought about by an increase of incoming fresh water during the rainy season. Further on, another striked area was reported on the west part of the lagoon and in the channels, more durable, around the Chenaque oil. drain. In several studies, oil has been reported, in the water column, sediments and oysters. A significant fact was the detection of heterotrophic and hydrocarbonoclastic bacteria in the Mecoacan lagoon, " important indicators used to detect oil impacted areas" (OAS-Conacyt in SUORE-CODEZPET, 1993).
In 1993, the Fisheries Ministry concluded that main oyster mortality in the Mecoacan lagoon was due to oil pollution. In February, 1992, less than two months after the oil spill caused by a failure in the PEMEX burner, the Fisheries Ministry, the Commission for the Development of Petroleum Zones in the state of Tabasco (CODEZPET), the Federation of Fishing Cooperative Societies and PEMEX made an inspection in which they detected a 70 to 80% mortality in the oyster population (CODEZPET, 1993). The fishermen asked for the judgment of the CODEZPET that said: the claims for the decrease in oyster production, because of water pollution related to petroleum activities in de Mecoacan lagoon, are valid...in average 10,000 tonnes are missing from the production for the years 1991-1993, 50% can be related to the hidrocarbons fenerated by the oil industry (CODEZPET, 1993). Although the institution acknowledged the impacts on the lagon originated by PEMEX, the state owned industry has not carried out neither the recommendations nor the signed agreements.
Scientific knowledge on the impact of petroleum is limited, even more in the tropics than in the temperate areas. Very little research has been done in the tropics on how oil concentrations, formerly considered very low, have affected the behavior of different species. It has been discovered that a great variety of animals suffer behavioral alterations that can affect their survival capacity, if exposed to low hydrocarbon concentrations. It has also been found that pollution by hydrocarbons can alter interactive competition among species, since more tolerant species began to outnumber the most vulnerable ones.
International scientific literature, referring to ecosystems similar to this lagoon, report that: the presence of hydrocarbons in the fine sediments of wetlands can persist for up to 100 years (Gundlach et al 1981; Teal and Howarth, 1984); sediment pollution is most persistent in low energy areas such as areas with low current flow (Brumer Et Al , 1971; Beslier Et Al, 1981); the affectation of one species must be assessed through studies that analyze indirect impacts through the food chain; plankton and bottom living organisms are generally more at risk near the coastline than in the open sea (NAS, 1985). Amphipods and oysters are the most sensitive to petroleum pollution
(Sanbere Et Al, 1980; Grassle Et Al, 1981; Elmgren & Frithsen, 1982: Teal & Howarth, 1984; Dauvin, 1987: Jackson Et Al, 1989: Dauvin and Gentil, 1990).